Lens holding tool

ABSTRACT

A lens holding tool includes a head portion and a pin that supports the head portion rotatably. The pin includes: a shaft portion having an exhaust outlet therein; a protruding portion that protrudes outwardly from the shaft portion; a sealing member disposed on the protruding portion; and a supporting portion that has a partially spherical shape and is disposed on a leading end of the shaft portion. The head portion includes: a workpiece receiving portion that holds a workpiece; an internal space that accommodates the protruding portion; an opening that has a diameter larger than a diameter of the shaft portion and smaller than an outer diameter of the protruding portion, the internal space communicating with an outside of the head portion through the opening; a suction hole through which the internal space communicates with the workpiece receiving portion; and an end receiving portion on which the supporting portion abuts.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a continuation of PCT international application Ser. No. PCT/JP2014/067040 filed on Jun. 26, 2014 which designates the United States, incorporated herein by reference, and which claims the benefit of priority from Japanese Patent Application No. 2013-224517, filed on Oct. 29, 2013, incorporated herein by reference.

BACKGROUND

1. Technical Field

The disclosure relates to a lens holding tool for holding a lens in grinding or polishing processing for the lens.

2. Related Art

When a lens is ground or polished so as to be a spherical shape, a lens holding tool is typically used to hold the lens (workpiece) rotatably. For example, Japanese Laid-open Patent Publication No. 07-205004 discloses a workpiece holder for supporting a workpiece, capable of supporting a pin rotatably and tiltably, and also performing vacuum suction to the workpiece.

In Japanese Laid-open Patent Publication No. 07-205004, the holder for holding the workpiece supports the pin. In addition, an air introducing passage and a groove portion are formed inside the pin and on an external circumference of the pin, respectively, so that a toric diaphragm is attached to the groove portion. Furthermore, a ring-shaped space (diaphragm chamber) that houses the diaphragm is formed in the holder (refer to FIG. 1 in Japanese Laid-open Patent Publication No. 07-205004). To process the workpiece, the holder holds the workpiece and a grinding tool or a polishing tool having a desired spherical shape (hereinafter, referred to as a processing tool) abuts on the workpiece. Then, the processing tool is rotated. Accordingly, the workpiece and the holder rotate in accordance with a movement of the processing tool. Therefore, the workpiece can be ground or polished in close contact with the processing tool. To convey the workpiece, when the inside of the holder (pilot chamber) is exhausted through the air introducing passage, the diaphragm is sucked so as to come into contact with a lower surface of the diaphragm chamber. As a result, the pilot chamber enters a vacuum state so that the workpiece is sucked by the holder through a suction port.

SUMMARY

In some embodiments, a lens holding tool includes a head portion that holds an optical member as a workpiece, and a pin that supports the head portion rotatably. The pin includes: a shaft portion having an exhaust outlet therein; a protruding portion that protrudes outwardly from the shaft portion; a sealing member disposed on the protruding portion; and a supporting portion that has a partially spherical shape and is disposed on a leading end of the shaft portion. The head portion includes: a workpiece receiving portion that holds the optical member; an internal space that accommodates the protruding portion; an opening that has a diameter larger than a diameter of the shaft portion and smaller than an outer diameter of the protruding portion, the internal space communicating with an outside of the head portion through the opening; a suction hole through which the internal space communicates with the workpiece receiving portion; and an end receiving portion that allows the supporting portion to abut thereon. A distance between an internal wall surface of the head portion and a bottom surface of the internal space decreases outwardly from an edge of the opening.

The above and other features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a structure of a lens holding tool according to a first embodiment of the present invention.;

FIG. 2 is a longitudinal sectional view of the structure of the lens holding tool according to the first embodiment of the present invention (with a pin pulled upward);

FIG. 3 is a longitudinal sectional view of a structure of a lens holding tool according to a second embodiment of the present invention;

FIG. 4 is a longitudinal sectional view of the structure of the lens holding tool according to the second embodiment of the present invention (with a pin pulled upward);

FIG. 5 is a longitudinal sectional view of a structure of a lens holding tool according to a third embodiment of the present invention;

FIG. 6 is a longitudinal sectional view of the structure of the lens holding tool according to the third embodiment of the present invention (with a pin pulled upward);

FIG. 7 is a longitudinal sectional view of the lens holding tool illustrated in FIG. 5 when axis deviation occurs;

FIG. 8 is a longitudinal sectional view of the lens holding tool illustrated in FIG. 7 with a pin pulled upward;

FIG. 9A is an explanatory longitudinal sectional view of a method for determining a diameter of an opening of a head portion in the lens holding tool illustrated in FIG. 5;

FIG. 9B is an explanatory top view of the method for determining the diameter of the opening of the head portion in the lens holding tool illustrated in FIG. 5;

FIG. 10 is an explanatory longitudinal sectional view of a method for determining a diameter of a sealing member in the lens holding tool illustrated in FIG. 5;

FIG. 11 is an explanatory longitudinal sectional view of a method for determining a height of the sealing member in the lens holding tool illustrated in FIG. 5;

FIG. 12 is an explanatory longitudinal sectional view of a method for determining a height of a pin fulcrum of the lens holding tool illustrated in FIG. 5; and

FIG. 13 is an explanatory longitudinal sectional view of a method for manufacturing a lens using the lens holding tool illustrated in FIG.

DETAILED DESCRIPTION

Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to these embodiments. The same references signs are used to designate the same elements throughout the drawings. The drawings are schematic, and a ratio and a relationship between sizes of respective portions are different from those of reality. A ratio and a relationship between respective sizes may also be different between the drawings.

First Embodiment

FIGS. 1 and 2 are longitudinal sectional views of a structure of a lens holding tool according to a first embodiment of the present invention. As illustrated in FIG. 1, the lens holding tool 100 according to the first embodiment is a tool that brings an optical member 1 as a workpiece into contact with a rotating processing tool 130 and holds the workpiece 1 so that the workpiece 1 is driven rotatably when a lens is manufactured from the optical member, and also sucks and holds the workpiece 1 so as to convey the workpiece 1 before and after the processing. The lens holding tool 100 includes a head portion 120 that holds the workpiece 1, and a pin 110 that supports the head portion 120 rotatably. Here, the processing tool 130 is a tool including a grindstone shaft 131 and a grind stone 132 that includes a processing surface 133 formed thereon. The processing surface 133 has a shape (for example, convex spherical shape) corresponding to a spherical shape (for example, concave spherical shape) into which the workpiece 1 is configured to be processed. The processing tool 130 is attached to a lens processing apparatus (not illustrated) so as to rotate around a central axis A13.

The pin 110 includes a shaft portion 111 made of metal or alloy that has a cylindrical shape, a protruding portion 112 that protrudes outward from the shaft portion 111, a sealing member 113 disposed on the protruding portion 112, and a supporting portion 114 formed on a leading end of the shaft portion 111. In the first embodiment, a rotational symmetry axis of the shaft portion 111 is defined as a central axis A11.

An exhaust outlet 115 is formed so as to extend along the central axis A11 in the shaft portion 111. One end of the exhaust outlet 115 is opened at an upper end surface of the shaft portion 111. At the side of the upper end surface, the exhaust outlet 115 is coupled to a vacuum suction apparatus not illustrated. The exhaust outlet 115 branches near the protruding portion 112. The exhaust outlet 115 is opened at a plurality of places on the side surface of the shaft portion 111 below the protruding portion 112. Note that, in the first embodiment, the exhaust outlet 115 is opened at two places on the side surface of the shaft portion 111. However, the exhaust outlet 115 may be opened at three or more places. Alternatively, the exhaust outlet 115 may be simply curved without branching so as to be opened at one place on the side surface of the shaft portion 111.

The protruding portion 112 has a disk shape including a notch 116 formed thereon. The sealing member 113 is fixed to the notch 116. The sealing member 113 has a ring shape with a circular cross section. The sealing member is formed of an elastic material, for example, silicone rubber (SR), nitrile rubber (NBR), chloroprene rubber (CR), ethylene-propylene rubber (EPDM), styrene-butadiene rubber (SBR), fluororubber (FKM), or butyl rubber (IIR). Note that, in the first embodiment, the protruding portion 112 and the shaft portion 111 are integrally formed. However, the protruding portion 112 and the shaft portion 111 may be separately formed, and then these may be combined. In this case, the protruding portion 112 and the sealing member 113 may be integrally formed of the above elastic material, or may be integrally formed of a hard material, such as Delrin (registered trademark) or Teflon (registered trademark).

The supporting portion 114 has a partially spherical shape. When the workpiece 1 is processed, as illustrated in FIG. 1, the pin 110 is arranged so that a spherical part of the supporting portion 114 abuts on a predetermined position of the head portion 120.

The head portion 120 has a cylindrical shape whose rotational symmetry axis is a central axis A12, and includes a head body lower portion 121 and a head body upper portion 122 which are screwed together by a threaded portion 123. At an end portion of the head portion 120 on the side of the head body lower portion 121, a workpiece receiving portion 124 is provided which is a concave region for holding the workpiece 1 and whose center lies on the central axis A12. A suction hole 128 is formed in the head body lower portion 121. An internal space 125 to be described later communicates with the workpiece receiving portion 124 through the suction hole 128.

Note that when the workpiece 1 is processed, a backing material 2 is attached to the workpiece receiving portion 124 in advance, and then the workpiece 1 abuts on the workpiece receiving portion 124 through the backing material 2. The backing material 2 is a sheet-shaped member that includes a resin material having a relatively high coefficient of friction, such as silicone rubber, or a material in which anti-slip treatment or adhesive treatment is performed to a surface of a base material made of a resin, such as polyester. The backing material 2 includes an opening formed therein in advance so that the opening is positioned at the suction hole 128.

The head portion 120 includes the internal space 125 that accommodates the protruding portion 112 of the pin 110. At an end portion of the head portion 120 on the side of the head body upper portion 122, an opening 126 is formed whose center lies on the central axis A12. The internal space 125 communicates with the outside of the head portion 120 through the opening 126. A diameter of the opening 126 is larger than that of the shaft portion 111 and smaller than an outer diameter of the protruding portion 112. An internal wall surface 127 on the periphery of the opening 126 has the same plane as a plane including the opening 126.

At a bottom portion of the internal space 125, an end receiving portion 129 for holding the supporting portion 114 of the pin 110 is formed. The end receiving portion 129 has a concave spherical shape with a position of a spherical center and a radius of curvature similar to those of the supporting portion 114. The supporting portion 114 abuts on the end receiving portion 129 so that the head portion 120 is supported so as to be tiltable and rotatable with respect to the pin 110. Hereinafter, the position of the spherical center for the end receiving portion 129 is referred to as a pin fulcrum Q1.

As described above, the diameter of the protruding portion 112 is larger than that of the opening 126. Thus, when the shaft portion 111 of the pin 110 is pulled upward as illustrated in FIG. 2, the head portion 120 is suspended and held. Accordingly, the sealing member 113 abuts on the internal wall surface 127 on the periphery of the opening 126 and seals the opening 126. In this state, operating the vacuum suction apparatus coupled to the exhaust outlet 115 decompresses the internal space 125 so that the workpiece 1 arranged on the workpiece receiving portion 124 can be sucked and held.

As described above, according to the first embodiment, the lens holding tool 100 includes the protruding portion 112 formed on the pin 110. The protruding portion 112 can be housed in the internal space 125 of the head portion 120. When the pin 110 suspends and holds the head portion 120, the sealing member 113 disposed on the protruding portion 112 seals the internal space 125. Therefore, sealability of the internal space 125 can be secured. Hence, by exhausting the internal space 125 through the exhaust outlet 115, the internal space 125 can be sufficiently decompressed. Even when, for example, the lens holding tool 100 holds and conveys the workpiece 1, a suction force can be securely maintained with respect to the workpiece 1.

Second Embodiment

Next, a second embodiment of the present invention will be described.

FIGS. 3 and 4 are longitudinal sectional views of a structure of a lens holding tool according to the second embodiment of the present invention. As illustrated in FIGS. 3 and 4, the lens holding tool 200 according to the second embodiment includes a head portion 220 that holds a workpiece 1, and a pin 210 that supports the head portion 220 tiltably and rotatably.

As in the first embodiment (refer to FIG. 1), the pin 210 includes an exhaust outlet 115 formed therein, a shaft portion 111 with a supporting portion 114 formed at a leading end, a protruding portion 211 that protrudes outward from the shaft portion 111, and a sealing member 213 disposed on a notch 212 of the protruding portion 211. Configurations and functions of the respective portions are similar to those in the first embodiment. In accordance with a shape of an internal space 224 of the head portion 220, sizes of the protruding portion 211 and the sealing member 213 are different from those in the first embodiment. In the second embodiment, a rotational symmetry axis of the shaft portion 111 is defined as a central axis A21.

As in the first embodiment (refer to FIG. 1), the head portion 220 has a cylindrical shape whose rotational symmetry axis is a central axis A22, and includes a head body lower portion 221 and a head body upper portion 222 which are screwed together by a threaded portion 223. Inside the head portion 220, the internal space 224 is provided that accommodates the protruding portion 211 of the pin 210. A workpiece receiving portion 124, a suction hole 128, and an end receiving portion 129 are formed in the head body lower portion 221. An opening 225 is formed in the head body upper portion 222. The internal space 224 communicates with the outside of the head portion 220 through the opening 225. A diameter of the opening 225 is larger than that of the shaft portion 111 and smaller than an outer diameter of the protruding portion 211. Configurations and functions of the respective portions are similar to those in the first embodiment. A shape of an internal wall surface 226 on which the sealing member 213 abuts when the pin 210 is pulled upward, is different from that in the first embodiment.

The internal wall surface 226 has a shape of a side surface of a circular truncated cone whose central axis is a central axis A22. The height of the internal wall surface 226 decreases outwardly from an edge of the opening 225. That is, the distance between the internal wall surface 226 and a bottom surface of the internal space 224 decreases outwardly from the edge of the opening 225. As illustrated in FIG. 3, a tilt angle of the internal wall surface 226 is preferably an angle at which a line passing through a pin fulcrum Q1 and a center O in a cross section of the sealing member 213 is orthogonal to the internal wall surface 226, when the head portion 220 is supported in a state where the central axis A21 of the pin 210 and the central axis A22 of the head portion 220 correspond to each other. In other words, diameters and heights of the protruding portion 211 and the sealing member 213 may be determined such that a perpendicular from the pin fulcrum Q1 to the internal wall surface 226 passes through the center O of the sealing member 213.

In the above lens holding tool 200, as illustrated in FIG. 4, when the pin 210 is pulled upward, the sealing member 213 abuts on the internal wall surface 226 so as to seal the opening 225. In this state, operating a vacuum suction apparatus coupled to the exhaust outlet 115 decompresses the internal space 224 so that the workpiece 1 arranged on the workpiece receiving portion 124 can be sucked and held.

In the second embodiment, since the internal wall surface 226 is formed at a slant, even when the pin 210 is pulled upward in a state where the pin 210 slightly tilts with respect to the head portion 220, the entire sealing member 213 can abut on the internal wall surface 226. As result, sealability of the internal space 224 can be sufficiently secured.

Third Embodiment

Next, a third embodiment of the present invention will be described.

FIGS. 5 and 6 are longitudinal sectional views of a structure of a lens holding tool according to the third embodiment of the present invention. As illustrated in FIGS. 5 and 6, the lens holding tool 300 according to the third embodiment includes a head portion 320 that holds a workpiece 1, and a pin 310 that supports the head portion 320 tiltably and rotatably.

As in the first embodiment (refer to FIG. 1), the pin 310 includes an exhaust outlet 115 formed therein, a shaft portion 111 with a supporting portion 114 formed on a leading end, a protruding portion 311 that protrudes outward from the shaft portion 111, and a sealing member 313 disposed on a notch 312 of the protruding portion 311. Configurations and functions of the respective portions are similar to those in the first embodiment. Determining sizes of the protruding portion 311 and the sealing member 313 in accordance with a shape of an internal space 324 in the head portion 320 is different from the first embodiment. In the third embodiment, a rotational symmetry axis of the shaft portion 111 is defined as a central axis A31.

As in the first embodiment (refer to FIG. 1), the head portion 320 has a cylindrical shape whose rotational symmetry axis is a central axis A32, and includes a head body lower portion 321 and a head body upper portion 322 which are screwed together by a threaded portion 323. Inside the head portion 320, the internal space 324 is provided that accommodates the protruding portion 311 of the pin 310. A workpiece receiving portion 124, a suction hole 128, and an end receiving portion 129 are formed in the head body lower portion 321. An opening 325 is formed in the head body upper portion 322. The internal space 324 communicates with the outside of the head portion 320 through the opening 325. A diameter of the opening 325 is larger than that of the shaft portion 111 and smaller than an outer diameter of the protruding portion 311. Configurations and functions of the respective portions are similar to those in the first embodiment. A shape of an internal wall surface 326 on which the sealing member 313 abuts when the pin 310 is pulled upward, is different from that in the first embodiment.

The internal wall surface 326 has a shape of a spherical zone whose center lies on a central axis A32. The height of the internal wall surface 326 decreases outwardly from an edge of the opening 325. That is, the distance between the internal wall surface 326 and a bottom surface of the internal space 324 decreases outwardly from the edge of the opening 325. Here, the shape of a spherical zone is a partial shape of the spherical surface cut and interposed by two parallel planes.

In the above lens holding tool 300, as illustrated in FIG. 6, when the pin 310 is pulled upward, the sealing member 313 abuts on the internal wall surface 326 so as to seal the opening 325. In this state, operating a vacuum suction apparatus coupled to the exhaust outlet 115 decompresses the internal space 324 so that the workpiece 1 arranged on the workpiece receiving portion 124 can be sucked and held.

When the workpiece 1 is processed, as illustrated in FIG. 5, positions and directions of the pin 310 and the head portion 320 are adjusted such that a central axis A31 of the pin 310 passes through a spherical center Q2 of a processing surface 133 of a processing tool 130. Then, the processing is started. However, as illustrated in FIG. 7, while the workpiece 1 is processed, the workpiece 1 is driven by rotation of the processing tool 130 and then the central axis A31 of the pin 310 sometimes deviates from the spherical center Q2 of the processing surface 133 (hereinafter, referred to as axis deviation). In this case, as illustrated in FIG. 8, when the pin 310 is pulled upward after the processing is completed, the head portion 320 is suspended and held while tilting with respect to the pin 310. However, in the third embodiment, since the shape of the internal wall surface 326 on which the sealing member 313 abuts has a spherical shape, the entire sealing member 313 can be brought into contact with the internal wall surface 326 regardless of a tilt of the head portion 320. Therefore, sealability of the internal space 324 can be secured.

Next, reference will be made to a method for determining a size of each of the portions in the lens holding tool 300.

First, with reference to FIGS. 9A and 9B, a method for determining a diameter D of the opening 325 of the head portion 320, will be described. FIG. 9A is a longitudinal sectional view of the lens holding tool 300 when axis deviation occurs. FIG. 9B is a top view of the lens holding tool 300 viewed in a direction of the central axis A32 of the head portion 320 (refer to the arrow in FIG. 9A). Hereinafter, in this case, a tilt angle (angle formed by a line passing through the spherical center Q2 and a pin fulcrum Q1, and the central axis A31) is defined as O. In that case, a width of the axis deviation (distance between the central axis A31 and a position A31′ of the central axis A31 when no axis deviation occurs) is defined as S.

A diameter and amplitude (distance between the central axis A31 and the central axis A32 in an opening surface) of the pin 310 in the opening surface (surface orthogonal to the central axis A32) are defined as E and B, respectively. When the tilt angle θ becomes maximal and the diameter D of the opening 325 satisfies the following expression (1), interference between the pin 310 and the head portion 320 can be avoided.

D>2(B+E/2)   (1)

When clearance w₁ between the head portion 320 and the pin 310 is taken into account, expression (1) can be rewritten as expression (1′). The clearance w₁ is any positive value.

D=2(B+E/2+w ₁)=2B+E+2w₁   (1′)

Here, a diameter C of the pin 310 is given by C=E·cos θ. When the pin 310 tilts, a height F of the pin fulcrum Q1 (length obtained by projecting a length between the spherical center Q2 and the pin fulcrum Q1 to the position A31′ of the central axis when no axis deviation occurs) is given by F=M·cos θ using the distance M between the spherical center Q2 and the pin fulcrum Q1. Accordingly, a relationship E=CM/F can be obtained.

The distance M is the sum of a distance H between a top surface of the workpiece 1 and the pin fulcrum Q1, and a radius of curvature R of the processing surface 133 (M=H+R). Hence, when a tilt occurs, the height F of the pin. fulcrum Q1 can be represented by F=√(M²−S²) using the distance M and the width S of the axis deviation. Note that a method for calculating the distance M will be described later.

Here, the amplitude B of the pin 310 and a depth A of the head portion 320 (distance between the opening surface of the head portion 320 and the pin fulcrum Q1) satisfy a relationship tan θ=B/A. The width S of the axis deviation and the height F of the pin fulcrum Q1 when a tilt occurs satisfy a relationship tan θ=S/F. Therefore, a relationship B=AS/F can be obtained.

Thus, the diameter D of the opening 325 is given by the following expression (2). In expression (2), any positive value 2w₁ is replaced with W.

$\begin{matrix} \begin{matrix} {D = {{2{{AS}/F}} + {{CM}/F} + {2w_{1}}}} \\ {= {{\left( {{2{AS}} + {CM}} \right)/F} + W}} \\ {= {{\left( {{2{AS}} + {CM}} \right)/\left. \sqrt{}\left( {M^{2} - S^{2}} \right) \right.} + W}} \end{matrix} & (2) \end{matrix}$

Alternatively, a relationship M=S/sin θ among the distance M, the width S of the axis deviation, and the tilt angle θ, is substituted in expression (2). Then, the diameter D of the opening 325 may be represented as a function of the tilt angle θ as in expression (2′).

D=2A·tan θ+C/cos θ+W   (2′)

Next, with reference to FIG. 10, a method for determining a diameter L of the sealing member 313 (diameter of a center position in the cross section) will be described. FIG. 10 is a longitudinal sectional view of the lens holding tool 300 when axis deviation occurs.

When the pin 310 tilts at a tilt angle θ, a diameter G of the opening 325 viewed in a direction of the central axis A31 (diameter of a tilted opening) is given by the following expression (3) using the diameter D of the opening 325 (refer to expression (2)).

G=D·cos θ  (3)

A radius of the sealing member 313 and a radius of the shaft portion 111 of the pin 310 are defined as P (P=L/2) and K (K=C/2), respectively. When the tilt angle θ becomes maximal and the diameter G of the tilted opening satisfies the following expression (4), even when the pin 310 is pulled upward, the sealing member 313 is prevented from coming off the opening 325. Thus, the opening 325 can be sealed.

G<P+K   (4)

Thus, the diameter L of the sealing member 313 can be given by expression (5).

L=2·P>2(G−K)

L>2(D·cos θ−C/2)   (5)

Next, with reference to FIG. 11, a method for determining a height Y (height at a central position in a cross section) of the sealing member 313 based on the pin fulcrum Q1, will be described. FIG. 11 is a longitudinal sectional view of the lens holding tool 300.

When the pin 310 tilts, a tilting radius V of the sealing member 313 can be given by the following expression (6) using a radius of curvature Q of the internal wall surface 326, clearance Z between the sealing member 313 and the internal wall surface 326, and a radius X of the sealing member 313 in a cross section.

V=Q−Z−X   (6)

Hence, the height Y of the sealing member 313 can be given by the following expression (7) using the tilting radius V and the diameter L of the sealing member 313 (refer to expression (5)).

Y=√(V ² −L ²/4)   (7)

Next, with reference to FIG. 12, a method for determining a height (distance M) of the pin fulcrum Q1 based on the spherical center Q2 of the processing surface 133, will be described. FIG. 12 is a longitudinal sectional view of the lens holding tool 300.

A height N of an end face 1 b of the workpiece 1 based on the spherical center Q2 of the processing surface 133, can be given by the following expression (8) using the radius of curvature R of the processing surface 133 and a processing radius U in the workpiece 1. Here, the processing radius U is a distance between an edge portion of a workpiece surface 1 a (boundary with the end face 1 b) and a rotating central axis of the workpiece 1 (central axis A32 of the head portion 320).

N=√(R ² −U ²)   (8)

A half of a central angle of the workpiece surface 1 a in the cross section illustrated in FIG. 12 (angle formed by a line from the spherical center Q2 to the end portion of the workpiece surface 1 a, and the central axis A32) is defined as β. The height N of the end face 1 b can then be given by the following expression (9).

N=R·cos β  (9)

The pin fulcrum Q1 is set at a point at which a tangent at the edge portion of the workpiece surface 1 a intersects with the central axis A32. Thus, the following relationship between the distance M and the radius of curvature R is satisfied.

R=M·cos β  (10)

Therefore, a relationship in the following expression (11) is satisfied.

cos β=N/R=R/M   (11)

Thus, the distance M between the spherical center Q2 of the processing surface 133 and the pin fulcrum Q1 can be given by the following expression (12).

$\begin{matrix} \begin{matrix} {M = {R^{2}/N}} \\ {= {R^{2}/\left. \sqrt{}\left( {R^{2} - U^{2}} \right) \right.}} \end{matrix} & (12) \end{matrix}$

As described above, according to the third embodiment, the shape of the internal wall surface 326 of the internal space 324 has a spherical shape. Therefore, even when the pin 310 is pulled upward in a state where the head portion 320 tilts with respect to the pin 310, the entire sealing member 313 can abut on the internal wall surface 326. As a result, sealability of the internal space 324 can be maintained and the workpiece 1 can be securely sucked and held.

In addition, according to the third embodiment, the size of each of the portions, such as the diameter D of the opening 325, is determined as described above. Thus, even when the head portion 320 tilts with respect to the pin 310 while the workpiece 1 is processed, no interference occurs between the pin 310 and the head portion 320. Therefore, a free rotation of the head portion 320 (driven rotation with respect to the processing tool 130) is not be interrupted. As a result, degradation of processing accuracy with respect to the workpiece 1 can be inhibited.

Next, reference will be made to a method for manufacturing a lens using the lens holding tools 100, 200, and 300 according to the above first, second, and third embodiments, respectively. An example of using the lens holding tool 300 will be illustrated and described below.

However, even in a case of using the lens holding tools 100 and 200, the same method can be used in order to manufacture a lens. Note that the backing material 2 is attached to the workpiece receiving portion 124 in advance before the lens is manufactured.

First, as illustrated in FIG. 6, in a state where the workpiece 1 abuts on the workpiece receiving portion 124 through the backing material 2, the pin 310 is pulled upward so that the sealing member 313 abuts on the internal wall surface 326. At the same time, the vacuum suction apparatus coupled to the exhaust outlet 115 is operated. As a result, the internal space 324 is decompressed so that the workpiece receiving portion 124 sucks the workpiece 1. In a state where the workpiece 1 is held as described above, the processing surface 133 of the processing tool 130 abuts on the workpiece surface 1 a of the workpiece 1. The processing tool 130 is attached to the lens processing apparatus not illustrated. The processing tool 130 is driven by the lens processing apparatus so as to rotate around the central axis A13.

After that, the vacuum suction apparatus is stopped. As illustrated in FIG. 5, the supporting portion 114 of the pin 310 abuts on the end receiving portion 129 so that the pin 310 supports the head portion 320. In this state, the lens processing apparatus (not illustrated) is operated so as to rotate the processing tool 130. As a result, the workpiece 1 and the head portion 320 holding the workpiece 1 are driven by the processing tool 130 so as to rotate. The workpiece surface 1 a of the workpiece 1 is then processed (ground or polished) by the processing surface 133.

After the processing of the workpiece 1 is completed, the pin 310 is pulled upward so that the sealing member 313 abuts on the internal wall surface 326. At the same time, the vacuum suction apparatus coupled to the exhaust outlet 115 is operated. As a result, the internal space 324 is decompressed again so that the workpiece receiving portion 124 sucks the workpiece 1. In this state, as illustrated in FIG. 13, the pin 310 is further pulled upward so as to suspend and hold the head portion 320, and separate the workpiece 1 from the processing tool 130. After that, the workpiece 1 is supported by, for example, a user's hand, and the vacuum suction apparatus is stopped so that the workpiece 1 is separated from the lens holding tool 300. As a result, the workpiece 1 (lens) subjected to desired processing can be obtained.

According to some embodiments, a sealing member is disposed on a protruding portion of a pin housed in an internal space of a head portion. Since a diameter of an opening of the internal space is smaller than an outer diameter of the protruding portion, the sealing member can seal the opening from the inside of the internal space. As a result, a suction force can be securely maintained with respect to a workpiece.

The first to third embodiments having been described above are only examples for carrying out the present invention. The present invention is not limited to the embodiments. The present invention can form various inventions by appropriately combining a plurality of constituent elements disclosed in the first to third embodiments. The present invention can be variously modified, for example, in accordance with specifications. Furthermore, other various embodiments can be implemented within the scope of the present invention.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. 

What is claimed is:
 1. A lens holding tool comprising: a head portion that holds an optical member as a workpiece; and a pin that supports the head portion rotatably, wherein the pin comprises: a shaft portion having an exhaust outlet therein; a protruding portion that protrudes outwardly from the shaft portion; a sealing member disposed on the protruding portion; and a supporting portion that has a partially spherical shape and is disposed on a leading end of the shaft portion, the head portion comprises: a workpiece receiving portion that holds the optical member; an internal space that accommodates the protruding portion; an opening that has a diameter larger than a diameter of the shaft portion and smaller than an outer diameter of the protruding portion, the internal space communicating with an outside of the head portion through the opening; a suction hole through which the internal space communicates with the workpiece receiving portion; and an end receiving portion that allows the supporting portion to abut thereon, wherein a distance between an internal wall surface of the head portion and a bottom surface of the internal space decreases outwardly from an edge of the opening.
 2. The lens holding tool according to claim 1, wherein when the pin suspends and holds the head portion, the sealing member abuts on the internal wall surface of the head portion so as to seal the opening. The lens holding tool according to claim 1, wherein the internal wall surface has a shape of a spherical zone.
 4. The lens holding tool according to claim 1, wherein the internal wall surface has a shape of a side surface of a circular truncated cone.
 5. The lens holding tool according to claim 4, wherein the sealing member is arranged such that, when the supporting portion abuts on the end receiving portion and a central axis of the pin matches a central axis of the head portion, a perpendicular from a spherical center of the supporting portion to the internal wall surface passes through a center of a cross section of the sealing member. 